This project proposes a three year neuropsychological study of patients with juvenile-onset insulin-dependent diabetes. The objective is to determine whether insulin-dependent diabetes over time has a significant influence on cognitive, perceptual, and motor functioning, of juvenile and adult diabetics. The possiblity of subtle brain dysfunction in this patient group is an area of study which has been comparatively neglected. Four groups of patients with juvenile-onset diabetes will be studied: 1. newly diagnosed juvenile-onset diabetics, with an age range of 10 to 18; 2. previously diagnosed child diabetics (duration of illness from 5 to over 10 years); 3. miscellaneous diabetics who have unusual problems such as severe retinopathy or relatively uncontrollable blood glucose fluctuation; 4. a group of adult diabetics of the insulin-dependent type with the disorder diagnosed for a minimum of 5 years. Appropriate child and adult control groups will be included. All patients will be administered standard intelligence measures (WAIS) as well as tests from the Halstead-Reitan Neuropsychological Battery, and a test of flicker and virbratory threshold. The finding of subtle deficits would contribute to earlier detection of effects of the disorder, as well as provide clinical information valuable in the management of the disease.